Field of the Invention
The present invention relates to a novel method for preparing bis(3-aminophenyl)disulphides of the general formula (I) and 3-aminothiols of the general formula (II)
in which the residues
X and Y are each independently hydrogen, linear or branched (C1-C4)-alkyl, linear or branched (C1-C4)-alkoxy, halogen or amino.
With preference, the residues
X and Y are each independently hydrogen, linear or branched (C1-C4)-alkyl, halogen or amino.
With particular preference, the residues
X and Y are each independently hydrogen, methyl and ethyl, fluorine and chlorine.
Bis(3-aminophenyl)disulphides of the general formula (I) and 3-aminothiols of the general formula (II) are important intermediates for preparing agrochemical active ingredients and pharmaceutical active ingredients.
Description of Related Art
The preparation of 3-aminothiols of the general formula (II) is already known. For instance, it is possible to convert 3-nitrophenylsulphonyl chlorides of the general formula (III),
in which the residues X and Y have the meaning stated above,to 3-aminothiols of the general formula (II), by reacting same with a large excess of a metal such as zinc (EP 2 226 312) or tin (J. Org. Chem. 21 (1956), 265-70) or with tin(II) chloride (Bioorganic & Medicinal Chemistry Letters 20 (2010) 1749-1751) in the presence of hydrochloric acid and an organic solvent.
In these reactions, in which both the nitro and the chlorosulphonyl groups are reduced in one step, large amounts of inorganic salts arise which have to be laboriously removed. This applies particularly to environmentally polluting metal salts such as zinc chloride and tin chloride. Furthermore, the chemical yields of this reduction method are not always satisfactory.
Multi-stage methods for preparing aromatic disulphides are also known, in which aromatic sulphonyl chlorides are first converted with sodium hydrogen sulphite to the sodium salts of the corresponding sulphinic acids, which are then reduced with sulphur dioxide to the diphenyl disulphides (EP 687 671; WO 2007/066844). These methods firstly require toxic gaseous sulphur dioxide and secondly do not always afford satisfactory yields. It is also known that diphenyl disulphides can be obtained starting from aromatic sulphonyl chlorides by reduction with triphenylphosphine (Tetrahedron Letters 50 (2009) 7340-2). Such a reduction can also be carried out by means of hydrogen bromide in a mixture of acetic acid and phenol (J. Fluor. Chem. 112 (2001) 287-95). These methods, however, only produce unsatisfactory yields and high amounts of waste. Most widely used is the reduction method with stoichiometric amounts of hydrogen iodide (J. Amer. Chem. Soc. 60 (1938) 2729-30; Organic Syntheses, Coll. Vol. 5(1973) 843; Vol. 40 (1960) 80; Synthesis 2003, 112-6). This method usually results in high yields but is very expensive and technically complex due to the large amounts of hydrogen iodide required and the need to dispose of, or recycle, the iodine formed.